This project involves determining the mutagenic, carcinogenic and/or teratogenic potential of an environmental agent commonly utilized for the treatment of neonatal hyperbilirubinemia; high intensity illumination with visible light or phototherapy. The proposed research will characterize the DNA-modifying potential of phototherapy by analyzing the physical chemical properties of several species of DNA exposed to photosensitizing agents and visible light in vitro. We will then determine if similar intracellular DNA modification occurs when prokaryotic and eukaryotic cells are exposed to light by analyzing the effect of light induced reactions on mutation frequency and the physical chemical properties of isolated DNA molecules. We will also determine if similar DNA modification occurs in the intact animal following exposure to high intensity visible light with and without added photosensitizing agents. Once the potential hazards of phototherapy have been identified, techniques will be developed to minimize these hazards and protect normal infants from potentially serious untoward sequelae.